1. Field of the Invention
The present invention relates generally to a hydraulic pressure control unit, and more particularly to the hydraulic pressure control unit which is applicable to a hydraulic pressure control system of an automobile for performing a steering control by braking and the like.
2. Description of the Related Arts
In a conventional hydraulic pressure control system of an automobile, electromagnetic valves have been employed for controlling the hydraulic pressure. As an embodiment, employed is a hydraulic pressure control unit having a housing with hydraulic passages defined therein, and a plurality of electromagnetic valves communicated with the hydraulic passages. One such hydraulic pressure control unit is disclosed in Japanese Patent Laid-open Publication No.7-248068, which corresponds to U.S. Pat. No. 5,474,108. In that unit, valve mechanisms of electromagnetic valves are accommodated in a housing, and solenoid coil portions are mounted on one wall of the housing, in parallel with each other.
Such hydraulic pressure control unit is used for various hydraulic pressure control systems, including a conventional system with a traction control system as shown in FIG. 7, for example. FIG. 7 illustrates a front-rear hydraulic braking system for use in a front drive vehicle with front wheels FR, FL driven. Wheel brake cylinders Wfr, Wfl, Wrr, Wrl are operatively mounted on the wheels including rear wheels RR, RL, respectively. Between these wheel brake cylinders and a master cylinder MC are disposed electromagnetic valves PC1-PC8 for controlling the hydraulic pressure, and electromagnetic valves TC1, TC2, TI1, TI2 for changing control modes. In FIG. 7, DP1, DP2 designate dampers, PV1, PV2 designate proportioning valves, RS1, RS2 designate reservoirs, and ECU designates an electronic controller.
In the above hydraulic pressure control system, is used a hydraulic pressure control unit similar to the one as disclosed in the Publication No. 7-248068, while each solenoid coil portion is formed in a cylindrical configuration, without being received in a rectangular case as shown in that Publication. For instance, twelve electromagnetic valves in total are mounted on the housing HP to form the hydraulic pressure control unit, as shown in FIG. 8. More precisely, the valve mechanism of each electromagnetic valve is accommodated in the housing HP, while its cylindrical solenoid coil portion is mounted on one wall of the housing HP to extend therefrom. In this case, provided that the outer diameters of all of the solenoid coil portions are equal, the twelve valves can be located with the neighboring valves being in contact with each other, as shown in FIG. 8.
In such a hydraulic pressure control system that performs a steering control by braking operation (i.e., an excessive oversteer restraining control and an excessive understeer restraining control), however, it is necessary to control the brake fluid pressurized at a relatively high pressure, with a brake pedal depressed. Therefore, in lieu of the electromagnetic valves TC1, TC2, TI1, TI2 for the traction control system as shown in FIG. 8, are employed such electromagnetic valves SC1, SC2, SI1, SI2 having solenoid coil portions of relatively large outer diameters as shown in FIG. 9. Supposing that the electromagnetic valves SC1, SC2, SI1, SI2 as shown in FIG. 9 are substituted for the electromagnetic valves TC1, TC2, TI1, TI2 as shown in FIG. 8, the housing HL in FIG. 9 is to be made larger than the housing HP in FIG. 8, which will result in increase in size of the hydraulic pressure control unit as a whole. That is, comparing with the housing HR as shown in FIG. 8, the housing HL is to be enlarged in the horizontal direction in FIG. 9, by a difference between the outer diameter of the valve SC1 or the like and that of the valve TC1 or the like, and in the vertical direction in FIG. 9, by a total of the difference between the outer diameter of the valve SC1 and the like, and that of the valve TC1 and the like (i.e., L1+L2 in total as shown in FIG. 9).
In the case where the pressure sensor PS is to be provided for detecting a condition for use in the steering control by braking system or the like, the unit will be necessarily enlarged further in the horizontal direction in FIG. 9.